PROJECT SUMMARY We aim to advance our current DNA nanoparticle (NP) delivery platform and gene expression to develop safe and effective therapies targeting important photoreceptor-associated ocular disorders caused by defects in large genes. We are merging knowledge in molecular bioengineering, nanoformulation, material science, eye biology/physiology and chemistry to accelerate essential steps for the generation of effective non-viral gene delivery platform for eye diseases. The NPs consist of single molecules of DNA compacted with poly-lysine- PEG polycation and have a diameter of 8-11 nm. Their small size coupled with cellular uptake via cell-surface nucleolin, which efficiently traffics the NPs to the nucleus, accounts for their ability to transfect post-mitotic photoreceptors. Using NPs has led to efficient expression of large genes, an essential prerequisite for targeting hard-to-rescue diseases of the retina. Although upper gene size limitation has not been established, the largest size tested in the lung was 20 kb and in the eye was ~14 kb making NPs an ideal alternative to AAVs for delivery of large genes. We have showed that NP treatment led to efficient transfection of ocular cells including photoreceptors and retinal pigment epithelium, exerted no toxic effects on the eye even after multiple injections, distributed throughout the subretinal space, and mediated appreciable structural/functional rescue in mouse models of retinitis pigmentosa, Leber?s congenital amaurosis, Stargardt?s and diabetic retinopathy. Effective gene expression without toxicity has also been achieved in baboon eyes. These proof- of-principle studies confirms the potential clinical significance of this technology and highlights the value of a large capacity, but emphasized the need for prolonged high levels of gene expression. Our main goal is to enhance photoreceptor uptake of NPs to achieve long-term therapeutic levels of expression of large genes for full phenotypic rescue. We propose to accomplish this by targeted vector engineering to boost expression levels along with NP-delivery platform to enhance their delivery from the vitreous to photoreceptors, achieve pan retinal distribution, promote episomal stability in the nucleus and prevent epigenetic silencing. Subsequently, we will test these optimized NPs/delivery platform(s) for their ability to mediate full phenotypic rescue in a large gene disease model; specifically the Abca4-/- model of Stargardt?s associated with the lack of ABCA4 gene. ABCA4 is a large gene which has not been fully rescued by traditional viral vectors and as a result development of targeted therapeutics for Stargardt?s has lagged. We plan in aim1 to engineer vectors that can achieve therapeutic levels of expression in photoreceptors and in aim 2 to develop effective NP- delivery platforms to enhance photoreceptor uptake of NPs from the vitreous. Aim 3 will test the efficacy of the best delivery platform of the most effective NPs for therapeutically-effective levels of expression in photoreceptors of Abca4-/- mice before and after the onset of the disease. In summary, results from this application will facilitate the advancement of DNA NP use for ocular diseases associated with large genes.